A pressure sensor using a metal diaphragm is disclosed in, for example, JP-A-2000-298071. The pressure sensor includes a package consisting of a metal housing having a fluid inlet and a resin connector having a terminal pin. The housing and connector are integrally jointed together. The package includes a metal stem and a sensing member. A portion of the metal stem is thin-walled to provide a metal diaphragm. The sensing member is mounted on the metal diaphragm through a glass paste (e.g., low-melting glass). The sensing member has a strain gauge formed by doping a semiconductor chip with p-type impurities and generates an electrical signal corresponding to pressure of the fluid introduced to the diaphragm via the fluid inlet. The electrical signal is transmitted to an external device via the terminal pin of the connector.
In such a pressure sensor, there is a fear that the semiconductor chip is detached from the stem (i.e., diaphragm) due to difference in thermal expansion coefficient between the semiconductor chip and the stem. Therefore, the stem is made of, for example, kovar, which has a thermal expansion coefficient similar to that of the semiconductor chip.
In some applications, kovar is not suitable for use in the housing in terms of resistance to corrosion. Further, the use of kovar is costly. Therefore, the housing is made of a different material than the stem. For example, the housing is made of stainless steel, aluminum, iron, or the like.
Since the housing and the stem are made of different materials, the housing and the stem are separate pieces. As a result, the number of parts required for the pressure sensor becomes increased, the structure of the pressure sensor becomes complicated, and the size of the pressure sensor becomes increased. Further, the seam between the housing and the stem needs to be sealed to prevent the fluid from leaking at the seam. Inadequate sealing of the seam causes the pressure sensor to operate improperly.